The present invention relates to automatic filling machines wherein empty cartons conveyed along a path are filled with liquid and sealed, and more particularly to liquid dispensing units for such machines.
High speed automatic filling machines such as is disclosed in U.S. Pat. No. 4,448,008, have been used for filling cartons with liquids, such as milk and juices.
These filling machines are required to dispense a predetermined quantity of liquid in each carton as it advances through the filling section of the machine. One type of dispensing unit that can be used is the double bellows type fluid handling apparatus such as that disclosed in U.S. Pat. No. 4,402,461. This patent discloses a dispensing unit having a pair of bellows interconnected by a tubular body containing a valve that controls the flow of fluid from the upper bellows to the lower bellows. The tubular body is mounted for reciprocating movement in an axial direction, and the end of each bellows that is connected with the tubular body moves with it. The opposite ends of the respective bellows are held stationary, so that the axial movement of the body in one direction compresses one of the bellows and expands the other. An actuator vertically raises the body to contract the upper bellows while simultaneously expanding the lower bellows. This action forces liquid from the upper bellows into the lower bellows. The actuator then lowers the body to expand the upper bellows while simultaneously contracting the lower bellows. This allows the upper bellows to be refilled with liquid and forces the liquid present in the lower bellows into a carton. The sequence is then repeated sequentially transferring liquid from a main source into the upper bellows, then into the lower bellows, and finally into individual cartons.
The actuator is described in U.S. Pat. No. 4,402,461 as an hydraulic or pneumatic ram. Control of the movement of the double bellows dispensing unit is accomplished by controlling the fluid pressure in the ram. Such a control device has the disadvantage that control of the ram involves frequent operation of several valves, components which are subject to wear and require periodic replacement. Another disadvantage of the prior art drive mechanism is that the fluid used to operate the ram is compressible. This causes the rate of displacement of the ram to decrease as the fluid pressure increases, and as a result, the stroke of the ram is difficult to adjust.